Wafer carrying device and wafer carrying method

ABSTRACT

A device for carrying a thin plate-like substrate such as a semiconductor wafer and controlling its position by floating it with an inert gas of low impurity concentration. A transferring unit and a controlling unit are respectively provided with gas nozzles for floating a thin plate-like substrate and with a gas exhausting and circulating system, and a plurality of them are in combination with each other in a sealing state. The controlling unit, further, has a vacuum suction hole at its controlling center, and is provided with nozzles for controlling the thin plate-like substrate in its radial and circumferential direction respectively and with nozzles for stopping the thin plate-like substrate or sending out it to the next unit too. On the bottom of a control space, grooves extending from the vacuum suction hole are formed for improving the positional accuracy of stopping the thin palate-like substrate, and they are closed on the insides of their circumferential part when the center of the thin plate-like substrate has coincided with the controlling center of the controlling unit.

TECHNICAL FIELD

The present invention relates to a sheet-like base or wafer carryingdevice and a sheet-like base or wafer carrying method, more particularlyto a sheet-like base carrying device and a sheet-like base or wafercarrying method by which a sheet-like base or wafer can be maintained ina stationary condition while it is floating and the accuracy of theamplitude of vibration caused in the sheet-like base or wafer can bemaintained in a range of 0.2 mm in a stationary condition, and furtherthe contamination of the sheet-like base or wafer can be prevented.

According to the present invention, the sheet-like base or wafer can becarried in an ultra-clean atmosphere. The sheet-like base or wafercarrying system by which the sheet-like base or wafer can be carried inan ultra-clean atmosphere is referred to as anultra-clean-floating-traffic-system (UCFT).

BACKGROUND ART

As a technique to carry a wafer by a fluid current, there is disclosedin Japanese Patent Publication Laid Open No. 38828-1980 such that agroove is formed on the surface of an orbit and by injecting fluid alongthe groove, a vacuum condition is created when the fluid is sucked intothe groove from a thin film of fluid.

This technique is excellent in its performance when it is applied to acarrying mechanism.

However, the inventors have found various following problems when theaforementioned carrying device is put into practical use.

First, it is difficult to maintain a wafer in a stationary condition ata predetermined position. For example, in the ease where the wafer isintroduced Into a film forming chamber, it is desired that thediscrepancy of the stationary position of the wafer from a predeterminedposition is in a range of ±0.2 min.

Therefore, it is necessary to guide the wafer to a predeterminedposition with an accuracy of ±0.2 min. Next, it is necessary to make thewafer stand still at the position without causing vibration In thewafer.

The inventors attempted to make the wafer stand still with the accuracyin accordance with the aforementioned conventional technique, however,it was difficult to maintain the wafer in a stationary condition withsuch accuracy. Further, there were no carrying devices capable of makingthe wafer stand still with the aforementioned accuracy.

After all, according to the conventional carrying device, vibrationswere caused in the radial, circumferential and horizontal directionswhen the wafer was in a stationary condition, and the amplitude of thevibration far exceeded 0.2 mm.

Secondarily, it was found that the predetermined characteristics of thewafer could not be necessarily obtained in the case where the wafer wascarried with the conventional carrying device and subjected toprocessing such as film forming or etching. For example, when an oxidefilm was formed on the wafer, its insulating property was not good, andwhen the wafer was subjected to etching, an etching with highselectivity could not be performed. As a result of investigations madeby the inventors to ascertain its cause, it was found that impuritiessuch as particles and moisture were deposited on the surface of thewafer deteriorating the processability. As a result of further variousinvestigations, it was found that such impurities had been deposited onthe wafer while the wafer was being carried. Especially, It was foundthat particles had been remarkably generated.

The aforementioned problems have not been known until now, being foundby the inventors for the first time.

OBJECT OF THE INVENTION

A primary object of the present invention is to provide a sheet-likebase carrying device and a sheet-like base carrying method by which asheet-like base can be maintained in a stationary condition with anaccuracy of ±0.2 mm, and further the contamination of the sheet-likebase can be prevented while being carried.

DISCLOSURE OF THE INVENTION

In order to solve the aforementioned problems, the present invention isto provide a sheet-like base carrying device in which a plurality oftransfer units having a transfer space to allow a sheet-like base toadvance linearly and a plurality of control units having a control spaceto control the movement of the sheet-like base, are combined in anairtight condition, said sheet-like base carrying device comprising: aplurality of jet holes for floating the sheet-like base, said jet holesbeing formed on the lower surface of the transfer space and connectedwith a gas supply system; an exhaust means provided at an appropriateposition in the transfer space so as to exhaust the gas from thetransfer space; an exhaust means provided at an appropriate position inthe control space so as to exhaust the gas from the control space; asuction hole formed in an approximately central portion on the lowersurface in the control space (the central portion is referred to as "acontrol center", hereinafter), said suction hole being connected with avacuum exhaust system; a groove formed on the lower surface of thecontrol space and extending from the suction hole; a plurality of jetholes for controlling the position of the sheet-like base in a radialdirection, the jet holes being formed on the lower surface of thecontrol space; a plurality of jet holes groups for controlling theposition of the sheet-like base in a circumferential direction, the jetholes groups being formed on the lower surface of the control space; aplurality of jet holes for floating the sheet-like base, said Jet holesbeing formed on the lower surface of the control space; and a pluralityof jet holes for stopping or carrying the sheet-like base to the nextunit, the jet holes being formed on the lower surface of the controlspace, wherein said groove is closed inside the periphery of thesheet-like base when the center of the sheet-like base has come to aposition above the control center.

Also, in a sheet-like base carrying method of the present invention whencarrying a sheet-like base with a sheet-like base carrying devicecomprising a plurality of transfer units having a transfer space toallow the sheet-like base to advance linearly combined with a pluralityof control units having a control space to control the movement of thesheet-like base in an airtight condition, is characterized in that acurrent of inert gas, the impurity concentration of which is not morethan several ppb, is used when the sheet-like base is carried with thesheet-like base carrying device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a carrying device relating to theexample of the present invention;

FIG. 2 is a partially broken view of a transfer unit relating to theexample of the present invention;

FIG. 3(a) is a perspective view showing the lower surface of the controlunit of the carrying device of the example of the present invention;

FIG. 3(b) is an enlarged view of the groove portion shown in FIG. 3(a);

FIG. 4 is a perspective view showing the arrangement of the jet holesfor floating the control unit of the carrying device of the example ofthe present invention;

FIGS. 5 and 6 are perspective views showing the arrangement of jet holesfor controlling in a radial direction of the control unit of thecarrying device of the example of the present invention;

FIG. 7 is a perspective view showing the arrangement of jet holes forcontrolling in a rotational direction of the control unit of thecarrying device of the example of the present invention;

FIG. 8(a) is a perspective view showing the arrangement of jet holes forstopping and sending of the control unit of the carrying device of theexample of the present invention;

FIG. 8(b) is a sectional view taken on line 1--1 in FIG. s(a);

FIG. 8(c) Is a sectional view taken on line 3--3 in FIG. (a);

FIG. 9 is a perspective view showing the example in which an ionneutralizing means is provided;

FIGS. 10(a), 10(b) and 10(c) are schematic illustrations showing theconcept of combination of transfer and control units; and

FIG. 11 to FIG. 22(b) are views showing the relation between a gas flowand a force applied to a wafer in the case where a pocket is provided inthe hole of a plate.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained in detail based on an example.It should be understood that the present invention is not limited by thespecific example.

FIG. 1 shows the entire structure of an example of the carrying devicefor a sheet-like base (for example, a wafer) according to the presentinvention.

The structure of each unit will be explained as follows.

The sheet-like base carrying device of this example essentially includesa transfer unit 1 having a transfer space to allow a sheet-like base toadvance linearly and a control unit 2 having a control space to controlthe movement of the sheet-like base, wherein a plurality of transferunits 1 and control units 2 are combined.

FIG. 2 shows the detail of the transfer unit 1. FIG. 2 is a partiallybroken view of the transfer unit 1.

The transfer unit 1 is essentially composed of a base mount 3 and atransfer space 4.

The transfer space 4 is basically formed from a surrounding member 5 andan upper surface of the base mount 3 and in the drawing, the transferspace 4 is open in the left and right, and a sheet-like base istransferred to an adjacent control or transfer unit through thisopening.

A plurality of jet holes for floating the sheet-like base are providedon the lower surface 6 of the transfer space 4, (the upper surface ofthe base mount 3). Each of the jet holes 7 for floating the sheet-likebase is connected with a gas supply system 8a.

In this example, each of the jet holes 7 is disposed in a plane which isperpendicular to the traveling direction of the sheet-like base (shownby character A or B in the drawing). Incidentally, in this example eachjet hole 7 is open to the lower surface 6, forming an angle of about 22°between the center line of the nozzle 7 and the lower surface 6. Ofcourse, this angle is not necessarily limited to 22°. Further, theangles of the jet holes 7 have not to be necessarily the same. Forexample, the angle of a jet hole being far away from the center line maybe small, and as it comes closer to the center line the angle of a jethole may be large.

In the case where gas is blown out from the jet holes for floating, thegas is blown out In the direction indicated by arrow "a" shown in FIG.2. Therefore, the gas is blown out against the back surface of asheet-like base passing through the transfer unit 1, so that thesheet-like base is prevented from being lowered and being contacted withthe lower surface 6.

A gas passage (not shown) connected with each jet hole 7 for floating isprovided in the base mount 3, and each jet hole 7 for floating iscommunicated with the gas supply system 8a through this gas passage.

As shown in FIG. 1, an exhaust means 9a to exhaust gas from the transferspace 4 to the outside is provided in the transfer space 4. In thisexample, the exhaust means 9a is disposed in the upper portion of thesurrounding member 5, and connected with a gas exhaust line 10.

In the present invention, only the jet holes approximately perpendicularto the traveling direction of the sheet-like base and open upward, areformed on the lower surface 6 of the transfer space 4, and there are nojet holes parallel or open diagonally to the traveling direction of thesheet-like base. Therefore, It is possible to ensure the floating heightof a wafer by a smaller amount of gas, and the traveling speed of thewafer can be prevented from increasing acceleratively and made to be aconstant speed.

Next, the control unit will be explained.

FIGS. 3(a) and 3(b) shows the entire structure of the control unit. Inthe same manner as the transfer unit 1, the control unit 2 isessentially composed of a control space and a base mount 3. In the samemanner as the transfer space, the control space is composed of asurrounding member and an upper surface of the base mount 3, althoughnot shown in FIGS. 3(a) and 3(b). However, the control space in thisexample, is open in four directions so that the sheet-like base can becarried to the right and left, and also upward and downward as shown inthe drawing.

A suction hole 11 is provided approximately in the control center of thelower surface of the control space 6 of the control unit 2, (the centerof the position where the sheet-like base is to be stopped).

The suction hole 11 is connected with a vacuum exhaust line 12, and thevacuum exhaust line 12 is further connected with an ultra-clean exhaustpump 13. Accordingly, when the ultra-clean exhaust pump 13 is operated,the suction hole 11 can be given a negative pressure through the vacuumexhaust line 12.

A groove 42 (a black portion in FIG. 3(a)) extending outside from thesuction hole 11 is provided on the lower surface of the control space.In this example, the groove 42 is symmetrically formed with the suctionhole 11 as the center.

This example is characterized in that the groove 42 is closed at theperiphery 14 of the sheet-like base or wafer 15. The inventors havefound that the configuration of the groove is important for stopping andmaking the sheet-like base or wafer 15 stand still with a high accuracyof ±0.2 mm, and the inventors have also found that it is important todetermine how far the groove 42 is extended. When the groove 42 isclosed at the periphery of the sheet-like base or wafer 15, it becomespossible to stop the sheet-like base with high accuracy although it isnot clear yet why the sheet-like base or wafer 15 can be stopped withhigh accuracy when the groove 42 is closed at the periphery of thesheet-like base or wafer 15.

The reason why the sheet-like base can not be stopped with a highaccuracy by the aforementioned conventional technique is assumed to beas follows:

According to the conventional technique, a negative pressure conditionis created when gas is blown out into the groove which necessitatescommunication of the groove with the outside in order to release thegas. For that reason, the vacuum condition created by the gas is notstable, so that the sheet-like base can not be stopped or maintained ina stationary condition with high accuracy.

An orientation flat 14a is formed in a portion of the periphery 14 ofthe sheet-like base or wafer 15 shown in FIGS. 3(a) and 3(b) so that thegroove 42 is accommodated at the periphery 14 even in the portion of theorientation flat 14a.

In the case where the sheet-like base is stopped at a predeterminedposition in the control space of the control unit, by performingevacuation through the suction hole 11, the sheet-like base can bemaintained in a stationary condition.

In order to detect the position of the sheet-like base 15, a detectionmeans such as an optical fiber tube may be provided in an appropriateposition.

On the lower surface 6 of the control space, are provided jet holes forfloating, jet holes for controlling in a radial direction, jet holes forstopping and jet holes circumferential direction, jet holes for stoppingand jet holes for ejection delivery.

In FIG. 4, the jet holes are shown for floating, omitting those afterthan for floating.

The jet holes for floating are provided all over the lower surface 6.

Each jet hole 17 (indicated by a black spot in FIG. 4) is open to thecontrol center. In this example, each jet hole 17 forms an angle of 22°with respect to the lower surface, however, it should be understood thatthe present invention is not limited to the specific example. That is,any angles may be adopted as far as the jet holes are open to blow outthe gas against the back surface of a sheet-like base when being abovethe control center to prevent the sheet-like base from coming intocontact with the lower surface.

These jet holes 17 for floating are connected with the gas supply system8b.

Next, with reference to FIGS. 5 and 6, the jet holes for controlling ina radial direction will be explained as follows.

The jet holes 16 for controlling in a radial direction are shown byblack dots in the drawing. These jet holes 16 for controlling in aradial direction are provided for adjusting a position of the sheet-likebase in a radial direction.

The jet holes 16 for controlling in a radial direction are pointing tothe control center, and in this example, they open onto the lowersurface 6 forming an angle of 22°. Therefore, when gas is blown out fromthe jet holes 16 for controlling in a radial direction, the position ofthe sheet-like base can be adjusted to the center.

These jet holes 16 for controlling in a radial direction are provided abit outside of the periphery 14 of the sheet-like base or wafer 15. Theorientation jet holes 16 at flat 14a are also provided a bit outside ofthe periphery 14 of the sheet like base or wafer 15. For example, in thecase of a sheet-like base or wafer of 150 mm, the jet holes 16 at theorientation flat 14a are preferably provided outside of the periphery ofthe sheet like base or wafer 15 by 1 to 3 mm in order to quickly adjustthe position in a radial direction, and more preferably the jet holes 16at orientation flat 14a are provided outside of the periphery by about 2mm.

In this example, 8 jet holes consisting of two jet holes (17a, 17a'),(17b17b'), (17c, 17c') and (17d, 17b') forming a pair are provided intotal. Of course, the present invention is not limited to the specificexample. Each pair is independently connected with each of the gassupply systems 8d, 8e, 8f and 8g. For example, in the case where thesheet-like base is shifted away from a predetermined position to theright upward in the drawing, its position can be adjusted to thepredetermined position when gas is blown out from the two jet holes(17a, 17a') disposed upward on the right. At this time, either the gasblown out from other jet holes is stopped or the gas is blown out with apressure lower than that of the gas blown out from the jet holes (17a,17a').

As described above, when the jet holes for controlling in a radialdirection are supplementary provided, it becomes possible to quicklyconduct a fine adjustment on the position of the sheet-like base. Inorder to improve the accuracy of position adjustment, it is preferablethat the jet holes are provided on the periphery of the sheet-like base.Especially, in the case of a sheet-like base having an orientation flat,it is preferable that the jet holes (17a, 17a') are disposed close tothe center correspondingly to the orientation flat.

Next, with reference to FIG. 7, the jet holes for controlling therotation will be explained as follows.

These jet holes 18a₁, 18a₂, 18a₃, 18a₄, 18b₁, 18b₂, 18b₃, 18b₄ forcontrolling the rotation are provided to control rotational direction.The jet holes for controlling the rotation are provided in the peripheryof the sheet-like base. From the viewpoint of adjusting the positionwith high accuracy in a short period of time, the jet holes forcontrolling the rotation are preferably provided on a circumference witha radius being 1/4 to 1/3 of the radius of the sheet-like base.

The jet holes for controlling the rotation are open facing thecircumferential direction, with some of them being open clockwise, andthe other are open counterclockwise. The jet holes open clockwise andthe jet holes open counterclockwise are respectively connected to theseparate gas supply systems 8h and 8i.

For example, in order to rotate the sheet-like base clockwise, the gassupply system 8h may be turned on so that the gas can be blown out fromthe jet holes opening clockwise.

Concerning the interval between pairs of jet holes (18a₁, 18b₁), (18a₂,18b₂), (18a₃, 18b₃) and (18a₄, 18b₄) for controlling the rotation, forexample, the interval between the jet holes 18a₁ and 18b₁ is preferably1 to 5 cm, and the jet holes for controlling the rotation are preferablydisposed in a range not more than 70 to 80% of the diameter of thewafer. When the jet holes are disposed the in the aforementioned range,the rotational direction can be controlled with high accuracy.

Next, with reference to FIGS. 8(a), 8(b) and 8(c), the jet holes forcarrying and stopping will be explained as follows. FIG. 8(a) is a planview. FIG. 8(b) is a sectional view taken on lines 1--1 and 2--2 in FIG.8(a). The sectional views taken on lines 1--1 and 2--2 are identical.FIG. 8(c) is a sectional view taken on line 3--3 and 4--4 in FIG. 8(a).The sectional views taken on lines 3--3 and 4--4 are identical. Theexample shown in FIG. 8, Is the case where the sheet-like base iscarried and stopped in the direction of X-axis or Y-axis. Also a part ofjet holes 19a₁ and 19a₃ for carrying and stopping are aligned in twolines and disposed on lines which are parallel to the X-axis. The jetholes 19a₂ and 19a₄ for carrying and stopping are aligned in two linesand disposed on lines which are parallel to the Y-axis. The other jetholes 20a₁ and 20a₃ are linearly disposed on X-axis. In the same manner,the jet holes 20₂ and 20a₄ are disposed on Y-axis. The jet holes 19a₁and 19a₃ for carrying and stopping are disposed in parallel with X-axisand open toward the control center. The jet holes 19a₂ and 19a₄ forcarrying and stopping are disposed in parallel with Y-axis and opentoward the control center. On the other hand, the jet holes 20a₁ and20a₃ for carrying and stopping are disposed in parallel with X-axis andopen to the opposite side from the control center, and the jet holes20a₂ and 20a₄ for carrying and stopping are disposed in parallel withY-axis and open to the opposite side from the control center. The Jetholes 19a₁ and 20a₃ are independently connected with the gas supplysystem 8j, and the jet holes 19a₂ and 20a₄ with the gas supply system81. The Jet holes 19a₃ and 20a₁ are independently connected with the gassupply system 8k, and the jet holes 19a₄ and 20a₂ with the gas supplysystem 8m.

Accordingly, for example, in the case where a sheet- like base iscarried in the direction of X-axis, gas is blown out from the jet holes19a₁ and 20a₃ for carrying and stopping when the gas supply system 8j isturned on, so that the sheet-like base is braked and then stopped. Inthis case, other gas supply systems are maintained off.

Next, in the case where the sheet-like base is carried in the directionof Y-axis, gas is jetted from the jet holes 19a₄ and 20a₂ for carryingand stopping when the gas supply system 8k is turned on, so that thesheet-like base is carried in the direction of Y-axis. In this case,other gas supply systems are kept turned off.

In the various jet holes described above, their inner diameters arepreferably not more than 1.0 mm, and more preferably not more than 0.8mm. When the inner diameters are determined to be not more than 1.0 mm,the amount of gas blown out from one jet hole can be stabilized, and asudden increase of said amount of gas can be prevented.

Also, at least the surfaces of the transfer and control units that comeinto contact with the gas are preferably mirror-like surfaces with Rmaxvalue of not more than 1 μm and without any processing affected zones.When the surface is formed in the aforementioned manner, it is possibleto prevent gas (for example, moisture) from being released from thesurface, which Is effective to prevent impurities from being mixed withthe gas for carrying. Therefore, it becomes easy to maintain theconcentration of impurities in the gas for carrying to be not more thanseveral ppb.

Especially when a passive state film is formed on the surface of astainless steel by heat treating the stainless steel (preferably to atemperature of 400° to 550° C.) in oxidizing gas having an impurityconcentration of not more than several ppb, not only the amount of gasreleased from the surface of the stainless steel becomes extremelysmall, but having also antiabrasion properties, generation of particlescreated by contact with gas for carrying can be substantially reduced.In this case, the thickness of the aforementioned passive state film ispreferably not less than 10 nm.

Furthermore, when the gas system is made in a closed circulating systemwhich will be described later, particles are mostly generated from thesliding surfaces inside the circulation pump and the vacuum exhaustpump. However, when the sliding surfaces are made with a mirrorlikepassive state film provided by heating a stainless steel sheet inoxidizing gas with impurity concentration of not more than several ppb,and the Rmax value of the mirrorlike passive state film being not morethan 1 μm, the generation of the aforementioned particles can beinhibited to not more than several ppb.

Next, the neutralization of electrical charge in the sheet-like basewill be explained as follows. The sheet-like base is sometimeselectrically charged when it Is carried or processed. Under the chargedcondition, particles tend to be deposited on the sheet-like base.Further, when the electrically charged sheet-like base is carried to thenext process, it is difficult to perform a predetermined process. Forexample, in the case where ions are injected into a sheet-like base orwafer which is electrically charged, it is impossible to inject ions theintended distance.

This example describes how to neutralize a sheet-like base electricallycharged while being carried. FIG. 9 shows its structure. In order toneutralize the electrical charge generated when a sheet-like base iscarried, an ion generation means 31 is provided in this example. The iongeneration means 31 may be composed, for example, of an ultraviolet rayirradiating lamp 32, a metallic mesh 33 (an electron emitting sectionfrom which electrons are emitted by the photoelectric effect), and anegative ion source gas 34. When the metallic mesh 33 is irradiated withultraviolet rays emitted by the ultraviolet ray irradiating lamp 32,electrons are generated by the photoelectric effect. These electronswhen combined with the negative ion source gas, generate negative ions.The negative ions are introduced into a transfer unit carried by acurrent of negative ion gas, and neutralize the electrically chargedsheet-like base. Incidentally, the metal used for the metallic mesh 33may be appropriately selected from metals capable of emitting electronsby the photoelectric effect when it is irradiated with ultraviolet raysand by combining with the wavelength of the emitted ultraviolet rays.For example, hydrogen gas or nitrogen gas, with impurity concentrationof not more than several ppb, is used for the negative ion gas source.When the electrically charged sheet-like base is neutralized by negativeions in the aforementioned manner, neutralization can be carried outwithout causing disturbance in the current of carrying gas. That is, inthe case where neutralization is conducted by the action of electrons, alarge amount of gas flow is required for sending the electrons to thesheet-like base. Accordingly, there is a possibility that the current ofcarrying gas is disturbed probably because the mass of electrons beingso small they easily flow into the inner wall, therefore it is necessaryto make a gas current going against for preventing the electrons fromflowing into the inner wall which necessarily requires a large amount offlow of the gas current. In contrast, the mass of negative ions is farlarger than that of electrons, so that the negative ions can be easilycarried to the sheet-like base by the gas current. Therefore, thecurrent of carrying gas is not disturbed.

In this example, the ion generation means is provided above the transferunit, however, it may be provided above the control unit, or above boththe control unit and the transfer unit. Although the current of carryinggas is hardly disturbed when the ion generation device is provided, theion generation device is preferably provided above the transfer unit inorder to further reduce its influence.

Next, the combination of the control and transfer units will beexplained.

The control and transfer units can be arbitrarily combined. For example,they can be combined In the manner shown in FIGS. 10(a), 10(b) and10(c).

It is preferable that they are combined through a metallic gasket or ametallic O-ring, and it is further preferable that the leakage of eachportion is not more than 10⁻¹⁰ [torr·1/s].

Next, the gas supply system and the exhaust system will be explained.

The vacuum exhaust holes 11 formed on the lower surfaces of the transferand control spaces are connected to the buffer tank 21 through theultra-clean vacuum exhaust pump 13. Also, the exhaust means provided inthe transfer and control spaces are connected to the buffer tank 21. Thegas accumulated in the buffer tank 21 after being made in a high puritygas by going from the buffer tank 21 through a circulation pump 22,filter 23 and gas purifying unit 24, the gas is supplied to the gassupply systems 8a to 8m. When the gas is supplied to the basic gassupply pipes of the gas supply systems 8a to 8m, new gas may be addedfrom a clean gas cylinder 25 in addition to the circulated gas which haspassed through the aforementioned gas passage.

Ultra-high purity inert gas (the concentration of impurities such aswater is not more than 10 ppb) is used for the gas to be supplied. Alsothe jetting speed of the gas is not higher than 200 m/sec. In the casewhere the jetting speed is higher than 200 m/sec, erosion Is caused bythe gas, which generates particles and deteriorates the processabilityof the sheet-like base.

As described above, since the gas system is separated from theatmosphere and the generation of impurities is inhibited inside thesystem, the impurity concentration of carrying gas can be alwaysmaintained to be not more than several ppb, and the contamination of thesheet-like base caused by impurities can be prevented while thesheet-like base is being carried.

Although the illustrations are omitted in this example, it is preferablethat this device is put on an appropriate vibration absorbing device inorder to absorb the vibrations transmitted from the outside.

[EXAMPLE OF OPERATING PROCEDURE]

In order to transfer a sheet-like base, the aforementioned sheet-likebase carrying device is operated in the following manner.

An example is taken in which a sheet-like base sent into a control unitfrom the direction X, is carried in the direction Y in FIG. 8(a).

DECELERATION AND STOP

When the sheet-like base sent into the control unit is detected,simultaneously the gas supply system 8j is turned on. Also, the gassupply system 8b is turned on. In this case, the gas supply system 8b isalways kept turned on during subsequent procedure.

When the gas supply system 8j is turned on, gas is blown out from thejet holes 19a₁, 20a₂ for carrying and stopping, and the sheet-like baseis decelerated by the action of the blown out gas. At this time, whenthe speed of the sheet-like base is detected, and the pressure or amountof the blown out gas is controlled in accordance with the detectedspeed, the sheet-like base approximately can be stopped in a positionwhere the center of the sheet-like base coincides with the controlcenter 11. By appropriately repeating the turn on and off of the gassupply systems 8j, 8k, 8l and 8m, or stepwise minute adjustment of theamount of blown out gas, the sheet-like base can be stopped while thecenter of the sheet-like base almost coincides with the control center11. At this time, the amount of blown out gas may be made smaller thanthat blown out from the gas supply system 8j when the sheet-like base isdecelerated.

CONTROL IN RADIAL DIRECTION

Next, the gas supply system 8c is turned on. At this time, the gassupply systems 8j to 8m are turned off. When the gas supply system 8c isturned on, gas is blown out from the jet holes 16 for controlling inradial direction, so that the center of the sheet-like base almostperfectly coincides with the control center.

CONTROL IN ROTATIONAL DIRECTION

Next, the gas supply systems 8h to 8i are turned on. By adjusting theamounts of gas sent from the gas supply systems 8h to 8i adjustment ofthe position of the sheet-like base with respect to the rotationaldirection while considering the crystal orientation of the sheet-likebase is performed.

SUCTION

Next, after the gas supply systems 8h to 8j have been turned off, theultra-clean exhaust pump 13 is driven to perform vacuum suction throughthe suction hole 11. By the suction through the suction hole 11, thesheet-like base Is stopped in a predetermined position. At this time,the gas supply system 8b maintains the condition of being turned on, andbecause the gas is always blown out from the jet holes 17 of gas forfloating toward the control center, the sheet-like base is maintained ina floating condition.

FINE ADJUSTMENT

By repeatedly turning on and off the gas supply systems 8d to 8g, andagain repeatedly turning on and off the gas supply systems 8h to 8i, theposition of the sheet-like base is controlled. At this time, theposition of the sheet-like base is controlled with the accuracy of notmore than ±0.2 min.

DELIVERY

Next, the gas supply systems 8c to 8i are turned off, and at the sametime the operation of the ultra-clean exhaust pump 13 is stopped. Then,the gas supply system 8k is turned on, and gas is blown out from the jetholes 19a₁ and 20a₂ of the gas for stopping and carrying, so that thesheet-like base is carried in the direction Y. At this time, the gassupply system 8a of the transfer unit located in the direction Y is alsoturned on, so that the sheet-like base is allowed to pass through thetransfer space in the transfer unit at a constant speed and carried tothe next control unit.

In order to conduct the aforementioned operation, It is necessary todetect the position (including the orientation) of the sheet-like base.Therefore, an appropriate detection means may be provided.

Next, a case will be described in which a pocket 50 is provided in eachjet hole of the plate 6 as shown in FIG. 11. When the pocket is providedin the manner described above, it is possible to reduce the amount ofgas to carry a wafer as shown in the graphs of FIGS. 12 to 16.

Also, it is preferable that a notch is provided in the jet hole as shownin FIG. 18.

Incidentally, the deformation of a wafer caused by gas pressure is shownin FIGS. 19 and 20.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to maintain asheet-like base in a stationary condition with an accuracy of ±0.2 mmwhile the sheet-like base is being floated, and also it is possible toprevent the contamination of the sheet-like base while being carried.

[DESCRIPTION OF REFERENCE SYMBOLS]

1 transfer unit

2 control unit

3 base

4 transfer space

5 surrounding member

6 lower surface

6a a plate

7 jet holes for floating

8a to 8m gas supply system

9a to 9b exhaust means

10 gas exhaust line

11 suction hole

12 vacuum exhaust line

13 ultra-clean exhaust pump

13 ultra-clean vacuum exhaust pump

14 periphery of a sheet-like base

14a a orientation flat

15 sheet-like base (wafer)

17 jet holes for floating

16 jet holes for controlling in a radial direction

17a, 17a', 17b, 17b', 17c, 17c', 17d, 17d' jet holes for fine adjustment

18a₁, 18b₁, 18a₂, 18b₂, 18a₃, 18b₃, 18a₄, 18b₄ jet holes for rotationalcontrol

19a₁, 19a₃, 19a₂, 19a₄, 20a₁, 20a₃, 20a₂, 20a₄ jet holes for sending andstopping

21 buffer tank

22 ultra-clean circulation pump

23 filter

24 gas purifying unit

25 clean gas cylinder

31 ion generation means

32 metallic mesh

33 negative ion source gas

42 groove

We claim:
 1. A wafer positioning and transporting apparatus comprising:aplurality of transfer units, each said transfer unit defining a transferspace for enabling linear travel of a said wafer, a first said transferspace having a first bottom surface; a plurality of control units, eachsaid control unit defining a control space for controlling positioningand movement of a said wafer, a first said control space having a firstlower surface; said plurality of transfer units and said plurality ofcontrol units sealingly interconnected; a first plurality of jet holesin said first bottom surface, said first plurality of jet holesconnected to a gas supply means for delivering gas to said firsttransfer space; a first exhaust means in said first transfer space forexhausting gas from said first transfer space; a second exhaust means ina first said control space for exhausting gas from said first controlspace, the central portion of the said first lower surface defining acontrol center for alignment with the center of a said wafer for controlof a said wafer; a suction hole disposed in said control center, saidsuction hole connected to a third vacuum exhaust means for exhaustinggas through said suction hole; a second plurality of jet holes in saidfirst lower surface for controlling the radial position of a said wafer;a third plurality of jet holes in said first lower surface forcontrolling the circumferential position of a said wafer; a fourthplurality of jet holes in said first lower surface for floatinglysupporting said wafer; a fifth plurality of jet holes in said firstlower surface for transporting and stopping a said wafer; and a groovein said first lower surface, said groove connected to said suction hole,said groove including a closed end, said closed end located inside theperiphery of a said wafer when a said wafer is positioned above andcentered with respect to said control center.
 2. The apparatus accordingto claim 1, wherein said first plurality of jet holes is substantiallyperpendicular to the direction of travel of a said wafer and openupwardly.
 3. The apparatus according to claim 1, wherein said secondplurality of jet holes is provided at the periphery of a said wafer whenthe center of the said wafer is positioned above and centered on saidcontrol center.
 4. The apparatus according to claim 1, wherein saidsecond plurality of jet holes is provided outside the periphery of asaid wafer when the center of the said wafer is positioned above andcentered on said control center.
 5. The apparatus according to claim 1,wherein said second plurality of jet holes includes a sixth plurality ofjet holes located at the periphery of a said wafer, and a seventhplurality of jet holes located outside the periphery of a said waferwhen the said wafer is positioned above and centered on said controlcenter, said sixth and seventh pluralities of jet holes eachrespectively connected to first and second gas supply systems.
 6. Theapparatus according to claim 1, wherein said third plurality of jetholes is provided inside the periphery of a said wafer when the centerof a said wafer is positioned above and centered on said control center,said third plurality of jet holes including an eighth plurality of jetholes which are open upwardly in a clockwise circumferential directionand a ninth plurality of jet holes which are open upwardly in acounterclockwise circumferential direction and wherein said eighth andninth pluralities of jet holes each are respectively connected to firstand second gas supply systems.
 7. The apparatus according to claim 1,wherein portions of said bottom surface and said lower surface include amirrorlike finish having an Rmax value of which is not more that 1 μm.8. The apparatus according to claim 7, wherein said mirrorlike finish iscomposed of a surface of a passive state film formed on a stainlesssteel sheet by heating in oxidizing gas having an impurity concentrationof not more than several ppb.
 9. The apparatus according to claim 1,wherein an ion generation means is provided in one of said transferspace and control space, said ion generation means generating ions bythe action of electrons emitted by the photoelectric effect.
 10. Theapparatus according to claim 1, wherein said third vacuum exhaust meanscomprises a vacuum exhaust pump, a circulation pump, filter and a gaspurifying device, and wherein said first and second exhaust means areconnected to said gas supply means through the said circulation pump,said filter and said gas purifying device, and wherein said gas supplymeans is sealed from the atmosphere.
 11. The apparatus according toclaim 10, wherein portions of said vacuum exhaust pump and saidcirculation pump which come into contact with gas are made of stainlesssteel, the surfaces of said portions including a passive state filmwhich has a mirrorlike surface, the Rmax value of said mirrorlikesurface being not more that 1 μm, said passive state film formed byheating stainless steel in oxidizing gas having an impurityconcentration of not more than several ppb.
 12. The apparatus accordingto claim 1, wherein the inner diameter of each said jet hole is not morethan 1.0 mm.